New synthetic route to soluble polyquinolines with tunable photophysical, redox, and electroluminescent properties

A new monomer bearing dialkyl groups, 3,3'-dinonanoylbenzidine, when copolymerized with diacetyl monomers gave six new alternating conjugated copolymers, poly(2,2'-arylene-4,4'-bis(4-alkylquinolines))s, which are soluble in organic solvents. The thermal, electrochemical, photophysical, and electroluminescent properties of the new polyquinolines varied with the arylene linkage, including p-phenylene, 4,4'-biphenylene, stilbene, 5,5'-bithienylene, bis(thienyl)vinylene, and 3,7-phenothiazinylene. The new conjugated polymers combined high glass transition temperature (110-254 degrees C) with quasireversible electrochemical reduction from which 2.72-3.00 eV electron affinities were estimated. The optical band gap varied from 2.19 to 2.86 eV whereas the photoluminescence emission maximum varied from blue-green (477 nm) to deep red (646 nm). Some of the new polymers with alternating donor-acceptor architecture showed strong intramolecular charge transfer. Electroluminescence of moderate brightness (up to 209 ed/m(2)) was achieved with blue-green, green, yellow, orange, and deep red colors depending on the arylene linkage of the copolymer. The new polyquinolines were also demonstrated as useful electron transport materials for the enhancement of polymer light-emitting diodes.